The authors describe the case of a 51-year-old male with Zollinger-Ellison syndrome manifested by epigastralgia, nausea, vomiting, hypergastrinemia and multiple endocrine neoplasia type 1. History included a Billroth II procedure for a perforated duodenal ulcer. Multiple metastatic liver lesions were found that were gastrin-negative and chromogranin-positive. Endoscopy revealed a large ulcerated gastro-jejuno-colonic fistula which was surgically repaired. Pre- and postoperative imaging studies, including the highly sensitive somatostatin-receptor scintigraphic scan using In-pentetreotide, have consistently failed to disclose other tumors. Recent reports indicate that most Zollinger-Ellison syndrome-associated gastrinomas are small, easily overlooked lesions located in the proximal duodenum rather than in the pancreas as formerly believed. In the present patient therapy with omeprazole and alpha-interferon has produced complete remission of the Zollinger-Ellison syndrome and a stabilization of tumor growth has occurred during the last 7 years, allowing the patient to live a normal life. This peculiar response to therapy is discussed.